1. The charger
The charger is integrated in the charging cradle. The charging method is not very sophisticated it is simply a constant current source. This means that the charger will continue to charge the accumulator with approximately 220mA even when it's already full. This will inevitable lead to overcharging of the accumulator which obviously does not seam to harm the NiCd accumulator excessively. One consequence of this charging method is however that the Mag Charger will get lukewarm once it is full.
The described charging method hasn't even changed on the new version of the charging cradle. Only the electronic circuit has been realized in SMD technology which makes it harder to repair. You can distinguish both versions through the connector type.
For both versions can be said that: If the LED is not shining, then the charging current is not flowing! It is more likely that this will be due to a bad contact of the collector rings to the charging pins, rather than a defect on the electronic circuit. In most cases it will be therefore sufficient to turn the Mag Charge in the charging cradle in order to remedy. If this does not help, try to clean the contact surfaces carefully. Don't use abrasives.
The circuits of both charger versions:
The voltage regulator LM317 is connected as a constant current source. If the 14kΩ-resistor would be bridged, then the charging current would be IC = 1,25V / 9,1Ω = 137mA. The adjustment pin current of ~50µA produces an additional voltage drop of 0,7V on the 14kΩ-resistor. The voltage on the 9,1Ω-resistor will therefore be 2V.
When assembling the ARXX025 take care that the LED-pins do not get in contact. This will rise the charging current to inadmissible high values and probably destroy the voltage regulator.
The principle of the new charger is the same than the old one. The LED has only been uncoupled from the charging regulation in order to avoid the above failure. The base resistor is integrated in the SMD-transistor. The reverse voltage protection diode has been replaced by an unidentified SMD-Chip.
Thanks to Geert de Vries I know now that the SMD-Chip is a N-channel MOSFET i.e. Fairchild FDC8601. MOSFETs can be used as reverse voltage protection with a low voltage drop.
2. Accumulator does not charge
If you run the Mag-Lite until the accumulator is overdischarged, then often one or more cells of the accumulator will drop there voltage to 0V. This state will even stay if you are charging the accumulator. You can recognize this problem on the fact that the overall voltage of the accumulator is lower than 5V.
Try to avoid to completely
emptying an accumulator, as this makes it suffer. However you will often
be able to "revive" the accumulator, by charging it during
a short time with a high current. Proceed as follows:
Connect the accumulator to a current-limited regulated voltage source. Ajust the voltage to 9V and limit the current to 2A. Charge the Mag Charger like this for half a Minute. In most case the defect cells will build up voltage again and you can continue charging the accumulator with the original charger. If the voltage continues to be clearly lower than 6V, than the defect cells cannot be recovered.
3. Alternative replacement accumulators
Alternative non-original 2600mAh NiCd- und 3600mAh NiMH-replacement accumulators can be found for example at Akkushop.de. Both types of accumulators are in use without any problems at my fire station since May, 2009.
4. Light intensity reduces after one minute
The light intensity reduces slightly after one minute even tough the accumulator is fine.
5. No replacement parts for the mid part
If you wonder why there are no spare parts for the mid part, the answer is that there is a limited 10 years warranty on that piece. We experienced for example that the contact spring to the positive electrode broke and the mid part was replaced.